1. Field of the Invention
The field of this invention relates to registration devices used for positioning work pieces on a work table and holding the same in place while the work piece is operated on. More particularly, this invention relates to registration devices that are attached to the tooling plate of the work tables of numeric controlled machine tools for automatically loading and unloading printed circuit boards and other work pieces for drilling or other machine operations.
2. Description of the Related Art
Printed circuit board (PCB) drilling machines are computer controlled machines having a table that moves in any X, Y plane; and a spindle that moves perpendicular to the table in the Z direction to drill holes in the PCB. On the X, Y table is a mounted plate, commonly called a tooling plate, onto which stacks of one or more PCBs are placed.
PCBs come in a variety of lengths, widths and thicknesses. However, PCBs always have at least two registration pins which are mounted in or through the PCB, so that the pins can be used to precisely mount the board into a known position after the board has been manually or automatically loaded onto the tooling plate. For automatic loading, the tooling plate has at least two types of clamps. A registration pin clamp is used to clamp the PCB's registration pin into a known registration position. The other clamp is a straight edge pin clamp, which is used to clamp the second registration pin into aligmnent with the known registration position at some point spaced apart from the registration position, dependent on the size of the PCB, to prevent rotation of the PCB on the tooling plate.
The registration pin clamping mechanism includes a registration block, which is aligned to the drilling machine for receiving the registration pin into a known registration position, enabling the programmer to use the registration position as a starting datum for creating a drilling program for the PCB. The registration pin clamping mechanism also includes a registration pin clamp which is a moving part that is biased against the registration pin and holds the pin in place against the registration block in the registration position. In order to achieve accuracy, the registration block must be securely mounted to the tooling plate.
The straight edge pin clamp includes a registration bar that is mounted to the tooling plate and aligned to the pin clamp registration block, and a moving edge clamp that clamps and unclamps the anti-rotation PCB pin at some point along the straight edge. Because PCBs come in many different sizes, the straight edge pin clamp must be in the shape of an elongated bar with a straight edge on the side which engages the registration pin so that it can clamp the anti-rotation PCB pin at any distance, regardless of the size of the PCB.
Drilling machines of this type are either automatically or manually loaded and unloaded. Automatic loaded machines come in two different designs. One design loads the PCB by lifting the PCB off of a stack and placing the PCB on top of the tooling plate. The other design slides one or more PCBs on top of the tooling plate into the designated position. In this type of design, the registration block moves out of position in order to enable the PCBs to be loaded into the proper position. Once the PCBs are in the proper position, the registration block will move back into position, and the PCBs will be clamped into place. As a result, maximum accuracy is not always achieved. The movement of the registration block can result in a slight misalignment of the registration block leading to random registration errors. The registration errors are detectable in the sub-micron level precision required for the accurate drilling of PCBs resulting in holes drilled in the wrong locations. Correcting the registration errors is a time consuming process that requires unloading the PCB and adjusting the registration block and registration bar.
For the foregoing reasons, there is a need for a registration system that will eliminate the registration errors introduced by movement of the registration block that are present when a PCB is automatically loaded onto a drilling machine.